Industrial sewing machines of the type disclosed in U.S. Pat. Nos. 4,449,464 and 5,309,854, both of which are hereby incorporated by reference herein, employ a biasing mechanism to normally bias the presser foot into a downward position against the periodic upward movement imparted to the presser foot by the reciprocating drive shaft. This biasing mechanism has heretofore been comprised of one or more helical compression springs encircling the presser foot lifting bar and contained within or by a cylindrical tube or guide rod.
Industrial sewing machines of the so-called “high lift” variety utilize such compression springs and are typically limited to operational speeds of about 3000 revolutions per minute. To achieve greater operational speeds more spring preload is required. However, more spring preload results in greater “wear and tear” on the sewing machine, the result being likely failure of a sewing machine component during sewing operations involving stitching over seams.
It is desirable to increase the operating speed of industrial sewing machines above 3000 revolutions per minute in order to increase productivity, but without jeopardizing the structural integrity of the sewing machine's components.